There remains a strong need for an inexpensive, highly reloadable all-plastic one-piece shotshell. One such shotshell is disclosed and claimed in our copending patent application, Ser. No. 117,580 filed by us on Feb. 1, 1980, and entitled ONE-PIECE SHOTSHELL.
Strengthening of sidewalls of thermoplastic tubing by orientation has been known for many years. In 1960, Diedrich disclosed in his U.S. Pat. No. 2,961,711 a method and apparatus for continuously making a biaxially oriented plastic tube which has been commonly used to produce shotshell casings from oriented plastic and has been known as Reifenhauser tubing.
In 1963, Covington et al disclosed in U.S. Pat. No. 3,103,170 a method for making a plastic tube in such a manner as to orient the sidewalls thereof, both axially and circumferentially to thereby greatly strengthen same.
Other U.S. Pat. Nos. such as Larson, 3,492,387; Eckstein, 3,786,755 and 3,855,381; and Sutcliffe, 3,514,468 disclose pertinent methods, apparatus and products but none of them contains a teaching of how to overcome the problems to which our present invention is directed.
Many of the above shotshell casings change shape and size after repeated firing. These changes result from the high pressure gases (generated upon firing) acting on the metal of the head and gradually distorting same, resulting eventually in a requirement for resizing. Since much reloading equipment includes no mechanism for resizing, the casing and head, upon such distortion, become as worthless to a shooter having such equipment as if actual rupture had taken place.
Some shotshell designs have had frequent failure of plastic sidewalls of the casings at the forward edge of the metal head. We have been successful in minimizing that problem by at least partially reversing the sidewalls upon themselves. We have effectively reduced the loss of strength occasioned by reheating of the plastic at that point in the sidewall where the greatest stress is produced by firing and have also eliminated tube growth problems.